1. Field of the Invention
The present invention relates to an electronically controlled engine mount which is disposed between a body and an engine of a vehicle and which is capable of arbitrarily changing its vibration transmission characteristics in correspondence with a state of vibration of the engine.
2. Description of Related Art
Recently, vibration transmission characteristics (e.g., dynamic spring constant and damping coefficient) of an engine mount has come to be electronically controlled to improve vehicular vibration characteristics. Japanese Utility Model Laid-Open Publication No. 4-39481 and Japanese Patent Application Laid-Open Publication Nos. Hei 4-185932, 5-306728, 6-330980 and 7-20439 disclose such devices.
While an actuator of the electronically controlled engine mount has been constructed using a PZT (piezoresistance element) according to Japanese Patent Application Laid-Open Publication No. 4-185932 and by using a voice coil using a rare-earth magnet recording to Japanese Utility Model Laid-Open Publication No. Hei 4-39481 described above, respectively, those components are expensive and it has been difficult to put them into practical use. Further, according to Japanese Patent Application Laid-Open Publication No. Hei 6-330980, although an actuator of an electronically controlled engine mount has been constructed by using a voice coil having an inexpensive ferrite magnet, its structure is still complicated and it has been expensive, so that it has not been suitable to be put into practical use.
Japanese Patent Application Laid-Open Publication Nos. Hei 5-306728 and 7-20439 disclose a relatively simple and inexpensive electronically controlled engine mount which uses a vacuum actuator and which reduces engine shake and idling vibration corresponding to engine operating conditions. However, because this engine mount is a so-called semi-active type engine mount which just switches vibration transmission characteristics between idling and other driving states, it has had a problem that it is unable to provide a sufficient idling vibration reducing effect.